Powering the BUS

1. less solar panels and less batteries = the most cost effective.

1.1. the charge controllers from MustPower take ANY input - mains power, solar panels, wind turbines, an exercycle? as well as a generator. As much as I'm against generators - they're noisy and annoying - they are totally handy if you can top your batteries up before they go too low and do damage to your THOUSANDS OF DOLLARS worth of batteries. We got our 160Ah batteries reconditioned for $200 each. So we have basically spent $1000 for 80Ah of decent 230v power use overnight.

1.2. ACCESS TO MAINS POWER means once you have a trickle charger, your batteries will stay topped up. This is their best state - sure it's good to fully use them before charging again but long-term, it's better they never go beyond 50%. For a $200 battery LCD unit you can keep up to date on levels and manually switch on the charger, anyway.

1.3. The end result: Solar PV array on land for off-grid (cost $2000+) completely offgrid with battery bank under $3k Access to mains power, but costs will be offset by solar and DC use. power bill <$80 a month instead of $200

1.4. the affordable interim: 4x 160Ah batteries $800 - $1200 8x 100w panels @ $1200NZ limitations: will need either generator or mains to charge 1-2hrs every few days,

2. inlet or not?

2.1. you don't need one to get access to power at a campsite. Just buy a trickle battery charger, and plug that into a three pin RV lead. The battery charger can be mounted in with the batteries underneath the bus out of the weather.

2.2. without an inlet, NONE of the electrical work needs to be certified. That means you can buy any parts you like from AliExpress, for 30% of the NZ retail price.

2.3. It also means you can do your own wiring. It sounds ominous, but in our situation I have quite a few extension cords leftover from catering and tools etc, they're already shielded and safe. If I need to, I can cut the ends off and add screw terminals to join them together. Then choose whatever PVC pipe you'd like to run the lengths under the bus. Unless you can fit runs of pipes on the inside?

3. A note about linear metres

3.1. Currently all of our 12V LEDs are wired in series. That means to get to Ames' room with power, I'll have to run cable there. I haven't really allowed for this, so the best way in is actually to start ANOTHER run of 12V cable from a junction box in our bathroom. I already know I have holes to drill for the floor due to drainage, and with the floor installed everywhere else, it's basically my only option! Unless I went up through under Ames' bed. But that sounds tricky. The point of wiring is to make it simple to find faults. Or replace faulty cables in the future. And to be safe.

3.2. 12V cables are speaker wire gauge - for low amp stuff like LEDs or car stereos. 12V cables under huge amp load - like 80A - will kill or injure someone a lot more easily, plus there's huge voltage loss over mid to long runs. I will have a few 60A cables to join my 12V batteries in series and parallel so they are 2x12---2x12--- as a 24V system and 1x12v for all lights and 12v stuff. It will need it's own charge controller and solar panel, but it means the lights are on a different system to the other stuff. If we drain all the mains we won't be without reading light or USB charging functions hehee.

3.3. The 60A battery connectors are $16 for two, so I'd need four or six or so just to join batteries together... about 1LM of copper... that's the same price for say, 50-100m of the thinner cable.

4. INPUT ---> CHARGE CONTROLLER / INVERTER ---> BATTERIES

4.1. 4x SOLAR PANELS, 36V @ 400W each. They run in parallel to charge ctrlr, which will receive THIS MUCH power

4.2. Open circuit voltage: a 12v panel will have 16-20V open circuit voltage, which gets regulated to 12v by the charge controller. It also makes sure the solar is an input only, not drawing power out after the sun goes.

4.3. The charge controller will then keep your batteries topped up. Depending on your system, the battery voltage has to match the system voltage, eg 12, 24, 36 (uncommon), 48. Most stick to 24 if their consumption isn't really going to go up to 2000w and stay there for long. Like our 2000w stuff is oven, blender, stuff that isn't on for long.

4.4. 24v or 48v? The biggest issue with 48V is the battery loss. The amps don't change, take for instance we have 5x 160Ah batteries. To run a 24V system we'd pair 2x12 and 2x12 with a spare. that'd give us 320Ah at 24V (it's 640Ah @12V but you'd be blowing something up electrically) or ...160Ah at 48V. Which seems ok if you're just running a fridge and some lights etc. But fridge + modem + laptop chargers and a load of washing / dryer at night means you'd hope the next day will be sunny enough. And that you have enough solar to fill them.

4.5. how many panels to how many batteries issue #1 - you can only use half the battery capacity. Yes. That means that now we effectively only have 80Ah to use, between the last ray of sun at ...5pm currently... to at least 8am. Out of those 15 hours, only three will really use much power, realistically. But it's dinner appliances, lights, fans, they all add up quick. So even with 4-5 batteries our system isn't big enough to handle a couple of days without sun.